Unsteady flow of igniter combustion-gas heating base bleed propellant by convection

The performance and launching accuracy of the vehicle with the base-bleed unit (BBU) depend strongly on the complex flow field characteristics and reignition delay time of the base bleed propellant in the combustion chamber of the BBU because the rapid depressurization process will occur in the BBU with a significantly altered flow field structure and induced extinguishment of the base bleed propellant located on both sides of the BBU when the vehicle is out of the muzzle at an initial time. However, the base bleed propellant will be reignited under the continuous convective heating effect of the igniter combustion-gas jet in the BBU at a later time. In this study, numerical simulations are carried out to investigate the coupling flow field characteristics and heating mechanism of the igniter of an actual BBU under a rapid depressurization process. Indeed, it is found that when the base bleed vehicle is out of the muzzle, the BBU experiences a rapid depressurization process due to the pressure difference between the combustion chamber of the BBU and the atmosphere, resulting in a strong unsteady flow field structure under the Kelvin–Helmholtz instability effect from the velocity difference between the igniter combustion-gas and gun propellant combustion-gas. Meanwhile, the high-temperature combustion-gas from the igniter is pressed on the end face of the igniter, and then, the axial expansion becomes quicker than the radial expansion with the development of the depressurization process. Afterward, the continuous convective heating effect of the igniter combustion-gas jet on the base bleed propellant occurs due to the direct contact of the high-temperature combustion-gas jet from the igniter with the surface of the base bleed propellant.